Rotating electrical machines such as vehicle alternators (dynamoelectric machines) (also commonly referred to as “generators”) having a stator secured within the housing of the machine and a rotor assembly that extends axially through the motor or generator are well known. The housing often includes two or more spaced apart frames which provide the main structural elements of the alternator. The frame closest to a pulley, which powers the alternator via a belt drive is commonly referred to as the drive end frame. The opposite frame is commonly referred to as the slip ring end frame. The frames support the rotor assembly comprising a rotor shaft with or without a connected rotor winding.
Alternators for vehicle use that mount electrical components such as brush holders, bridge rectifiers and voltage regulators on an outer wall of the slip ring end frame are also known. To protect these electrical components from external damage, a cover is provided that can be attached to the slip ring end frame. The cover is commonly formed of plastic material such as a glass filled nylon and is a one-piece molded part.
Currently there are two methods used to attach the protective cover for an alternator. One method includes self-attachment of the cover to the slip ring end frame of an alternating current generator by means of latch arms extending from the cover. The latch arms are molded into the plastic cover. The end frame has a plurality of circumferentially spaced openings that are spaced so as to receive the latch arms of the cover when the cover is attached to the end frame. Each of these openings has an edge that is defined by two intersecting surfaces. One of these surfaces is parallel to the longitudinal axis of the end frame and the other surface is inclined or slanted so that it is at an angle to the longitudinal axis of the end frame.
To assemble the cover to the end frame, the latch arms are pushed into the openings in the end frame and as this occurs the latch arms are forced or sprung radially outwardly. When the latch arms have been fully pushed into the openings, they spring back radially inwardly due to their resilient characteristic. When the latch arms spring back radially inwardly, the slanted surfaces on the latch arms are forced into tight engagement with the slanted surfaces on the end frame. Because of this, an axial force is developed that tends to force end surfaces of the cover into tight engagement with surfaces on the end frame. Further, when the latch arms spring back radially inwardly, the surfaces on the latch arms that are parallel to the longitudinal axis of the cover are forced into tight engagement with the surfaces on the end frame that are parallel to the longitudinal axis of the end frame. Because of this, the cover is radially clamped to the end frame and is prevented from moving radially with respect to the end frame.
For most applications this method works well and the cover remains tightly secured to the end frame and cover rattling does not occur during use throughout the life of the product. However, on extreme vibration applications, such as on a diesel engine, or with applications that must operate for an extended time, the plastic snaps are prone to creep, which leads to a loose cover. The loose cover may create a rattle noise, and if severe enough, may even fall off after wearing the latch/frame interface.
Another method includes using threaded fasteners that are threaded into the end frame or by threaded fasteners that are threaded into nuts. Typically three screws or studs with nuts are used to hold the cover in place. This method overcomes the creep issue, but it also adds material and assembly costs.
Accordingly, a method and apparatus are desired that overcomes the cost issues with using a plurality of threaded fasteners while also offering the same type of long, term snugness on high vibration and extended time applications provided by the plurality of threaded fasteners.